Preparation of 2-mercapto thiazolines



Patented June 10, 1941 PREPARATION OF Z-MERCAPTO- THIAZO- LINES- PaulSwithin Pinkney, Wilmington, Del., assignor to E. I. du Pont de Nemours& Company, Wilmington, 1321., a corporation of Delaware No Drawing.Application February 21, 1940, Serial No. 320,009

12 Claims.

This invention relates to the preparation of 2mercapto thiazolines andparticularly from N -(2-hydroxyalkyl) amides of carboxylic acids.

Z-mercapto thiazolines are well known compounds. It has been found thatsuch Z-mercapto thiazolines are excellent accelerators for thevulcanization of rubber. It was early proposed to prepare thesecompounds from alkanolamines and carbon disulfide. Such early methodsgave very low yields, and hence the compounds have not been commerciallyavailable until very recently.

It is an object of the present invention to provide a new and economicalprocess for preparing 2-mercapto thiazolines. Another object is toprovide a method for preparing Z-mercapto thiazolines from relativelycheap starting materials.

A further object is to provide a one-step process for preparingZ-mercapto thiazolines from N-(Z-hydroxyalkyl) amides of carboxylicacids. Other objects are to advance the art. Still other objects willappear hereinafter.

The above and other objects may be accomplished in accordance with myinvention, which comprises heating an N -(2-hydroxyalkyl) amide of acarboxylic acid with carbon disulfide at temperatures above 50 C. in thepresence of water or caustic alkali or both, employing at least 2 molesof carbon disulfide for each mole of the 2-mercapto thiazoline to beproduced. I have found that, by such process, the 2-mercapto thiazolinesare produced directly in a single step and. in good yields.

The 2-hydroxyalky1 amides, which may be advantageously employed asstarting materials in my process, may .be prepared by the action ofcarbon monoxide and ammonia on 1,2-glycols, such as ethylene glycol, athigh temperatures and pressures in the presence of a catalyst.

The amount of carbon dlsuliide employed may be varied over wide limits,but preferably is from 2 to 3 moles for each N-(2-hydroxyalkyl) amidegroup present. Thus, if the amide of a monocarboxylic acid is employed,from 2 to 3 moles of carbon disulfide will be employed. If the diamideof a dicarboxylic acid is employed, from 4 to 6 moles of carbondisulfide will be employed for each mole of the diamide. Smallerproportions of carbon disulfide may be employed, but usually withdecreased yields of 2-mercapto th-iazoline. One mole of hydrogen sulfideand one mole of carbon oxysulfide appears to be formed for each mole of2-mercapto thiazoline produced. Accordingly, it is essential to employat least 2* moles of carbon disulfide for each mole of the 2-mercaptothi-azoline to be produced.

The amount of water or caustic alkali or both may be widely varied.However, for best results, at least 1 mole of water 'or caustic alkalior both should be used for each mole of Z-mercapto thiazoline to beproduced. The best results are obtained in the presence of both waterand caustic alkali, and particularly when 1 molecule of caustic alkaliis present for each carboxylic acid group. In other words, when an amideof a monocarboxylic acid is employed, the best results are obtained ifat least 1 mole of caustic alkali is present for each mole of the amide.When the amide of a dicar-boxylic acid is employed, the best results areobtained with 2 moles of caustic alkali for each mole of amide. Watermay be em- .ployed alone. However, it is preferred to employ an alkalinecatalyst with the water. Caustic alkali in small amounts appears tofunction as a catalyst. Alkali metal formates also are desirablecatalysts to be employed with water.

Solvents, other than water, may be employed if desired. However, thebest results appear to be obtained in the absence of such addedsolvents.

The temperatures employed for carrying out the reaction may be widelyvaried. The temperatures should be above 50 C. and generally not higherthan about 200 C. When N-(Z-hydr-oxyethyl) amides are employed, thetemperatures should preferably be between about C. and about 130 C. WhenN-(Z-hydroxyalkyl) amides, containing 3 or more carbon atoms in thealkyl group, are employed, the temperatures should be between about C.and about 200 C. The time required for completion of the reaction willgenerally vary inversely with the temperature, the reaction taking placewithin shorter periods of time at the higher temperatures. Usually from6 to 10 hours will be sufficient.

It is generally advisable to carry out the reaction in a closed vessel,particularly when the higher temperatures are employed. The use of sucha closed vessel will result in the reaction being carried out atsuperatmospheric pressures produced by the gaseous reaction products andthe vapors of the solvents and reacting ingredients employed. WhenN-(2-hydroxyethyl) amides are employed, the reaction may be carried outat atmospheric pressures under reflux at the lower temperatures,although the use of a closed vessel and the higher temperatures isgenerally preferred. Whenthe higher homologues of theN-(2-hydroxye'thyl) amides are employed, a

closed vessel is required because of the higher temperatures employed.

When the reaction is completed, the reaction mixture is preferablydissolved in caustic alkali and the solution filtered to removeimpurities. The filtrate is then acidified to precipitate theZ-rnercapto thiazoline which may be washed with water and dried. The2-mercapto thiazoline may be further purified by crystallization from anappropriate solvent, such as alcohol or toluene or the like. Othermethods of separating the 2- mercapto thiazoline from the reactionmixture may be employed.

In order to illustrate my invention more clearly, the preferred modes ofcarrying the same into eifect and the advantageous results obtained, thefollowing examples are given in which the parts are by weight:

Example I A mixture of 27 parts of Z-hydroxyethylformamide, 46 parts ofcarbon disulfide and parts of water was placed in a steel bomb andheated at 120 C. for a period of 10 hours. The reaction mixture wasfiltered and the insoluble solid product was purified by solution in 10%sodium hydroxide solution, treatment with decolorizing charcoal, andreprecipitation with dilute hydrochloric acid. The yield of 2-mercaptothiazoline thus obtained was 3.2 parts (9% of the theoretical).

Example III The reaction was carried out as in Example 11 using 27 partsof 2-hy-droxyethylformamide, 46

parts of carbon disulfide, 20.4 parts of sodium formate, and 50 parts ofwater. The yield of Z-mercapto thiazoline was 8.7 parts (24% of thetheoretical) Example IV The reaction was carried out as in Example IIusing 31 parts of Z-hydrOxyethylacetamide, 46 parts of carbon disulfide,16 parts of sodium hydroxide, and 50 parts of water. The yield of2-mercapto thiazoline was 16.5 parts (46% of the theoretical).

Example V The reaction was carried out as in Example II using 23 partsof 2-hydroxyethylbenzamide, 21 parts of carbon disulfide, 6.6 parts ofsodium hydroxide, and 75 parts of water. The yield of Z-mercaptothiazoline was 0.8 parts (5% of the theoretical) Example VI A mixture of27 parts of Z-hydroxyethylformamide, 45.5 parts of carbon disulfide,13.5 parts of sodium hydroxide, and 50 parts of water was placed in asteel bomb (200 cc. capacity) and heated at 120 C. for a period of sixhours. The reaction mixture was filtered and the solid product was takenup in parts of warm 10 per cent sodium hydroxide. The clear filtrate,obtained by filtering the cloudy solution through kieselguhr, wasacidified with dilute hydrochloric acid. The resulting precipitate of2-mercapto thiazoline was collected on a filter, washed with water anddried. The yield of 2-mercapto thiazoline, M. P. 106 C., was 19 parts(53% of the theoretical).

Example VII A solution of 18 parts (1 mole) of 2-hydroxy ethylformamideand 38 parts (2.5 moles) of carbon disulfide in 75 parts of 95% ethanolwas placed in a steel bomb and heated at 170 C. for a period of 6 hours.After evaporation of volatile material from the reaction mixture, theresidue was taken up in 75 parts of 10% sodium hydroxide solution andwarmed with decolorizing charcoal. The mixture was filtered hot and thecooled filtrate was acidified with dilute hydrochloric acid and cooledfurther to ensure complete precipitation of the product. The precipitatewas washed on the filter with cold water and air dried. The yield of2-mercapto thiazoline was 7.6 parts (32% of the theoretical).

Example VIII A mixture of 18 parts of 2-hydroxyethylformamide, 38 partsof carbon disulfide, and 9 parts of sodium hydroxide was placed in asteel bomb and heated at C. for 10 hours. The reaction mixture was takenup in 75 parts of water, treated with decolorizing charcoal, andfiltered hot. The filtrate was acidified with dilute hydrochloric acidwith cooling, and the resulting precipitate of Z-mercapto thiazoline wasfiltered out and washed on the filter with cold water. The yield was11.6 parts (48% of the theoretical).

It will be understood that the above examples are given for illustrativepurposes only. Many variations and modifications may be made therein andin the conditions employed. Many other N-(2-hydroxyalkyl) amides ofother carboxylic acids may be substituted for those given in theexamples. Preferably, the amides are the amides of monocarboxylic acids,particularly of unsubstituted carboxylic acids, that is, those acidswhich, except for the carboxylic groups, consist of carbon and hydrogen.I particularly prefer the amides of the aliphatic acids and especiallyof the unsubstituted monocarboxylic aliphatic acids. Among theN-(Z-hydroxyalkyl) amides, which will be suitable starting materials forpracticing my invention, are the N-(2-hydroxyalkyl) amides derived fromthe following hydroxyalkyl amines and carboxylic acids:

Hydroxyalkyl amines Acids 1-amino-2-cthanol 2-amino-l-propanol.Z-amino-l-butanoL. 1-amino-2-butanol.. 3-amino-2-butanoll-amino-2-methyl-2-propanol 3-amino-2-pentanol. Isobutync2-amino-l-pcutanol. Valerie. 2-amino-3-pentanol.. Oxalic.l-amino-2-mothyl-2-butanol Glutarle Maleic.

3'amino-2-methyl-2-butanoL Fumaric.

2-amino-2ethyl-l,B-propanediol 2-amino-3-hexanol Tartnric.2amino-2-methyl-3-hexanol Adipic.

3 ammo 2-methyH-heptanuh. Cyclohexylucctic.2-amino-2-propyl-l,3-propanediol Cyclohcxylcurboxylic 3-amino-1-heptanolBenzoic.

2-amino-2-isopropyl-l,3-propnnedicl Phenylacctic.

3-amino-3-methyl-4-heptunol Phenylbutyric. 3-amin0-3-1nethyl-2-pentanolfi-amino-eicctanol It will be apparent that my invention provides asimple, one-step process for the preparation of useful materials. Thestarting materials are relatively cheap and are readily prepared fromcheap raw materials. The process permits the direct conversion ofN-(2-hydroxyalkyl) amides into Z-mercapto thiazolines without it beingnecessary to isolate and purify any intermediate compound.

I claim:

1. The process of preparing a Z-mercapto thiazoline which comprisesheating an N-(2- hydroxyalkyl) amide of a carboxylic acid and carbondisulfide at temperatures above 50 C. in the presence of at least onemember of the group consisting of water and caustic alkali, employing atleast 2 moles of carbon disulfide for each mole of the 2-mencaptothiazoline to be produced.

2. The process of preparing a 2-mercapto thiazoline which comprisesheating one mole of an N-(2-hydroxyalkyl) amide of a carboxylic acidwith about 2 to about 3 moles of carbon disulfide in a closed vesselunder superatmospheric pressures at temperatures of from about 90 C. toabout 200 C. in the presence of at least one mole of a member of thegroup consisting of water and caustic alkali.

3. The process of preparing a Z-mercapto thiazoline which comprisesheating one mole of an N-(Z-hydroxyalkyl) amide of an unsubstitutedmonocarboxylic aliphatic acid with about 2 to about 3 moles of carbondisulfide in a closed vessel under superatmospheric pressures attemperatures of from about 90 C. to about 200 C. in the presence of atleast one mole of a member of the group consisting of water and causticalkali.

4. The process of preparing a 2-mercapto thiazoline which comprisesheating one mole of an N-(2-hydroxyalkyl) amide of an unsubstitutedmonocarboxylic acid with about 2 to about 3 moles of carbon disulfide ina closed vessel under superatmospheric pressures at temperatures of fromabout 90 C. to about 200 C. in the presence of water containing at leastone mole of a member of the group consisting of caustic alkali andalkali metal formate.

5. The process of preparing a 2-mercapto thiazoline which comprisesheating one mole of an N-(Z-hydroxyethyl) amide of a carboxylic acidwith about 2 to about 3 moles of carbon disulfide in a closed vesselunder superatmospheric pressures at temperatures of from about 90 C. toabout 200 C. in the presence of at least one mole of a member of thegroup consisting of water and; caustic alkali.

6. The process of preparing a 2-mercapto thiazoline which comprisesheating one mole of an N-(2-hydrozwethyl) amide of an unsubstitutedmonocarboxylic acid with about 2 to about 3 moles of carbon disulfide ina closed vessel under superatmospheric pressures at temperatures of fromabout C. to about 200 C. in the presence of at least one mole of water.

7. The process of preparing a 2-mercapto thiazoline which comprisesheating one mole of an N-(2-hydroxyethyl) amide of an unsubstitutedmonocarboxylic acid with about 2 to about 3 moles of carbon disulfide ina closed vessel under superatmospheric pressures at temperatures of fromabout 90 C. to about 200 C. in the presence of at least one mole of anaqueous solution of caustic alkali.

8. The process of preparing a 2-mercapto thiazoline which comprisesheating one mole of an N-(2-hydroxyethyl) amide of an unsubstitutedmonocarboxylic aliphatic acid with about 2 to about 3 moles of carbondisulfide in a closed vessel under superatmospheric pressures attemperatures of from about 90 C. to about 200 C. in the presence ofwater containing at least one mole of a member of the group consistingof caustic alkali and alkali metal formate.

9. The process of preparing Z-mercapto-thiazoline which comprisesheating one mole of N- (Z-hydroxyethyl) formamide with about 2 to about3 moles of carbon disulfide in a closed vessel under superatmosphericpressures at temperatures of from about 90 C. to about C. in thepresence of at least one mole of a mem ber of the group consisting ofwater and caustic alkali.

10. The process of preparing 2-mercapto thiazoline which comprisesheating one mole of N-(2-hydroxyethyl) formamide with about 2 to about 3moles of carbon disulfide in a closed vessel under superatmosphericpressures at temperatures of from about 90 C. to about 130 C. in thepresence of at least one mole of Water.

11. The process of preparing Z-mercapto thiazoline which comprisesheating one mole of N-(2-hydro-xyethyl) formamide with about 2 to about3 moles of carbon disulfide in a closed vessel under superatmosphericpressures at temperatures of from about 90 C. to about 130 C. in thepresence of water containing at least one mole of a member of the groupconsisting of caustic alkali and alkali metal formate.

12. The process of. preparing Z-mercapto thiazoline which comprisesheating one mole of N-(Z-hydroxyethyl) formamide With about 2 to about 3moles of carbon disulfide in a closed vessel under superatmosphericpressures at temperatures of from about 90 C. to about 130 C. in thepresence of at least one mole of an aqueous solution of caustic alkali.

PAUL SWITI-IIN PINKNEY.

